1. Field of the Invention
The present invention relates to a communication system, a relay node and a user node therein, and a method thereof.
2. Description of the Related Art
In the related art, communication systems are based on an end-to-end communication model, such as the client-server model, or the peer to peer model. In these models, communication sessions are controlled at nodes at the two ends of a communication link, and relay nodes need to be provided for control of each communication session. In such a communication system, communication terminals functioning as end-nodes, such as mobile terminals, may provide or make requests for various services.
In a mobile communication system, however, because mobile terminals can be freely moved, and the quality of the electrical signals changes frequently, the radio link between a mobile terminal and its party is apt to be disconnected. In addition, a radio link generally has a narrower communication bandwidth than a fixed link such as a cable, therefore, if the communication link is disconnected, the mobile terminals may not continue to provide or make requests for services, or the service is stopped. This problem occurs not only in the case of mobile terminals in a mobile communication system, but also in the case wherein one of the end nodes of a communication link is not connected constantly. For a service provider that is not constantly connected, when the link is disconnected, the service provider cannot respond to any request nor provide any service.
In other words, in a communication system wherein the communication link is not constantly connected, provision of and request for services cannot be smoothly performed.
In the related art, methods involving Web servers or mobile file servers are used to overcome difficulties in an unstable communication system utilizing such a non-constantly connected link, such as a radio link. However, these methods are used only for specified types of service and protocols, and are not applicable to the communication systems described above.